Broadband jammer utilizing a duplex power distributed amplifier



G. DE SOCIO BROADBAND JAMMER UTILIZING A DUPLEX Jan. 8, 1963 POWER DISTRIBUTED AMPLIFIER 2 Sheets-Sheet 1 Filed Feb. 5, 1959 w LMU BY LUM..

Jan. 8, 1963 G DE socio 3,072,848

BROADBAND JAIIVIER UTILIZING A DUPLEX POWER DISTRIBUTED AMPLIFIER Filed Feb. 3, 1959 2 Sheets-Sheet 2 JNVENToR.

wl @0,966 af soc/o BY W Patented dan. 8, i963 George de Socio, Baltimore, Md., assigner to the United States of America as represented by the Secretary of tite Air Force Fied Feb. 3, 1%9, Ser. No. 796,936 3 Claims. (Ci. S25- 132) The present invention relates to a duplex power supply and particularly to a broad band jammer fed by a duplex distributed amplifier power.

The principies of distributed amplification including a description of the basic theory of operation of such systems, was presented by Percival in British Patent 460,562, dated July 15, 1936, and discussed in the article entitled Distributed Amplification appearing in the Proceedings of the LRE., vol. 36, page 956 (1948), by Ginston, Hewlett, Jasberg and Noe.

In conventional amplifiers, where the tubes are connected in cascade, the total voltage gain is the product of the gains of each individual tube. Since the product of gain and band width has an upper limit for any given tube, the gain per tube i ust be reduced in order to increase the band width. Connecting the tubes in parallel does not improve the condition because the circuit capacity, which limits the band width, is approximately doubled by the parallel grid-cathode interelectrode capacities.

According to the principles of distributed amplification, a number of tubes are arranged so that the individual tubes are driven, not at the same time, but in sequence by an input signal, with their outputs being delayed and then added. In this arrangement the grid to ground capacities of the tubes form the capacitive elements of a lumped constant delay line and coils connected consecutively between the grids form the inductive elements. The plates are connected to another delay line with the smic propagation constant.

As a signal travels down the grid line it causes a wave to propagate in both directions at each successive plate. The waves in the forward direction add in phase and are applied to a load and those in the reverse direction are absorbed in terminating resistors. The total gain is the sum of the gains of individual tubes.

The heretofore known distributed amplifiers have been effective in wide band amplication but have been ineiicient because of the loss of power in the reverse terminations.

The present invention improves the efficiency of broad band distributed amplifiers by feeding a load at both the forward and reverse terminations of the plate line. This is of particular value where two loads must be fed simultaneously in the same phase relation. By applying the input voltage at the center ofthe grid line a voltage will be propagated in both directions. lf the two halves of the amplifier are alike the reverse and forward loads will be equal and in phase.

ln the use of jamming it is desirable to cover a maximum of area with a wide band in order to prevent questing radars from securing a fix. By mounting a pair of antennas so that they do not see each other and by feeding the pair of antennas with the wide band power produced by a duplex distributed amplifier a maximum of coverage in area and band width can be secured.

In the construction according to the present invention a pair of radiating antennas are mounted on the opposite sides of a supporting vehicle and connected to the respective ends of the plate line of a broad band distributed amplifier by equal lengths of supply cable and an input voltage connection is applied centrally of the grid line.

lt is accordingly an object of the invention to provide an improved jamming system.

It is another object of the invention to provide a distributed amplifier having an improved efficiency.

Other objects and advantages of the invention will be apparent from the following description taken in conjunction with the accompanying drawing in which:

FIG. l is a schematic diagram of a broad band jammer having a duplex distributed amplifier.

FIG. 2 is a possiblewiring diagram for the amplifier sections;

FIG. 3 is a fragmentary schematic diagram showing the manner of mounting the jammer on a vehicle;

FIG. 4 is a fragmentary view'of a modification; and

FIG. 5 is a wiring diagram of the system shown in FIG. 1.

In an exemplary embodiment according to the invention antennas llti and 12 are mounted in substantially hidden relation with respect to each other on the body of a vehicle such as the airframe 14 of an aircraft. Antennas 1d and 12 are connected to respective ends 16 and 1S of a plate line 2G of a distributed amplifier presently to be described. The antennas l@ and l2 are connected by substantially identical cables 22 and 24.

The distributed amplifier as is well known is constituted by a plurality of amplifier tubes connected in spaced relation to a delay line having suitable reactors 23 connected between each of the tubes 3@ and its adjacent tube with a final termination at each end and reactors 32 and 345 having one-half of the reactance of the reactors 2S. The tubes 3@ are distributed in a right and left section each containing one-half of the number of tubes in the amplifier. The amplifier tubes 3ft are controlled from a grid line 4t) having a connection 42 intermediate the ends thereof forv applying control impulses to the grid line. Herein the connection is shown as the tube 44 having a controlled grid d6 to which the control impulses are applied. The current to the plate 4S will be drawn from the grid line 4d and the impulse will be propagated in each direction up the grid line d@ with the capacitance to ground of the grids of the tube 35D forming lump capacitance of a delay line and reactors Sti forming lumped reactance so that the delay characteristics of the grid line 4b and the plate line 2@ are identical. The grid line is terminated by reactors 52 and 54 having one-half the reactance of the intermediate reactors 5b. Also, reactors d6 and 58 at the connection ft2 are likewise of one-half the reactors of the intermediate reactors Sti. The reverse and forward ends of the grid line it? are terminated to ground by means of impedances 6ft and 62.

While the individual units of the distributed amplifier may be constructed of any of the well known filter units the connection shown in FlG. 2 has been found satisfactory. The tube 3? is provided with a control grid 64 connected to ground through a capacitor 66 and biased from a suitable negative source through an impedance 68. The plate '70 is connected to ground through a capacitor .72 and supplied with positive potential from any suitable source. The plate is connected to the plate line 2@ and the positive DC. potential is blocked from 8,072, 3 the plate line 2li' by means of suitable blocking capacitors 7d and '7o. The grid line 4G likewise contains blocking capacitors 78 and Y For the analysis of the duplex amplifier, the following are good assumptions: (l) the lines are lossless, (2) am- 5 plitiers are linear andare current generators, (3) no reliections exist at the terminals of the transmission lines, (4) lines are constant K filters with identical propagation constants or phase shifts, (5) no interaction between grid and plat-e lines. p Consider an input voltage wave e0 at i2 propagating in both directions along grid line 40, voltages appearing at each amplifier tube are delayed in proportion to the number 'of phase shift sections traversed. For our analysis We will consider only the voltage wave appearing at the plates 70 of each amplifier tube 30. These voltages combine with both the forward wave and the reverse wave.- We shall combine ,these waves to show the nature of the output into the antennas and l2.

EFAOW The voltage wave existing at the left antenna due to the reverse wave from the right section is:

ERzAe@s N+1i|6i N+si p erwan-ii] which-reduces to Y sin N qS E A i2N. Y R e sin qs adding E+ER=E5 the total voltage at the left antenna.

sin N qS normalizing Et and taking magnitude derives the expression for the magnitude of the voltage existing at the antenna.

Due to symmetry, this voltage exists at the right antenna also. The above voltage is due to the parallel feed of the grid line. However, if a balanced input to the grid line is available, a slight modification results due to the fact that ER=ER for the parallel case. 70

The normalized magnitude of Et for balanced input is then:

Eta:

sin No Y sin 2Nf,5

N sin o) Em: N sin 1;

lt is evident that for a balanced input, the signals at the antenna are opposite in phase, and could be used for a push-pull power output.

The magnitude of the voltages existing at the antennas is not constant with frequency and slight cancellation reinforcement due to the reverse waves produce a gain tolerance in the band. The approximate shrinkage for each type amplifier is as follows:

TABLE I N fi,3 ab Percent 3 db, 3 db, coverage percent percent There is a gain below f1 for parallel feed, and a loss for balanced feed. b There is a loss below f2 for parallel feed, and a gain for balanced iced.

in general, the low frequency rise in gain is not particuflarly serious in a distributed amplifier, and as noted above in Table I, the high frequency cutoff is reduced only slightly above 4 tubes.

in actual cases where some line 'attenuation is present, the reverse waves are attenuated more than the forward waves and will thereby reduce the gain tolerance in the band. The reverse waves on the line cancel each other at all points on the Vline for a parallel input.

lf the antennas i6 and l2 are not completely isolated from each other, a disturbance will exist on the plate line depending upon coupling and phase shift between the antennas.

The voltage gain of the amplifier section is roughly halved, but the total power delivered to both antennas is increased over an ordinary distributed amplifier, if the driving voltage e0 remained constant.

Effects on performance of this amplier due to mismatches at the termination are no different than that for an ordinary distributed ampliiier.

As indicated above, the mutual coupling between Vthe antennas lt and l2 affects not only the pattern, but the driving impedance of the antennas. The amount of conpling will determine the amount of signal fed from one antenna to the other. The energy fed back into the antenna will propagate eventually in a reverse direction on the plate line 2,6 of the distributed amplifier. This will produce the same effect as a mismatched load. If we'consider that the mismatches are identical, then the reverse traveling waves willV be equal and opposite in phase and there will be as a result standing waves on the plat-e line Ztl. The two waves will cancel in the center of the line Vand partially cancel elsewhere. Standing waves on the plate line willnot aiiect the performance of the amplifier. It should be mentioned here that each antenna is connected through equal length cables.

The other factor to be considered, of course, is the antenna pattern. T here are a few interesting possibilities for antenna arrangement as applied to jamming. Since it is desired to cover as much space as possible, particularly forward and below and to the sides, two antennas mounted on a large airframe will cover about twice as much space as one. lf the two antennas cannot see? each other, there will be small pattern interference forward. lf the antennas are mounted horizontally and symmetrically opposite at the ncse of the aircraft, the patterns could be just touching at the frame center of the aircraft and a null will occur there. This is not obleetionable since we .are not usually aimed directly at the antenna of the receiver to be jammed. lf slight overslapping of the patterns occur, multiple lobes will appear at the forward line. Such an installation is shown in EEG. 3; although each antenna does not see the other, there is a 'zone of interference forward, and depending upon the contour of the ship, the antennas can be placed to minimize this zone.

Another type of antenna which could be fed by such an amplier could be an omnidirectional antenna 90 with crossed polarization as shown in FIG. 4 where coupling between phases is minimized. Such an antenna mounted below the aircraft would give full coverage with elliptical polarization.

Another possibility for application of this amplifier is to push-pull oscillography in which the phases are inverted by a balanced input. Here the plate lines are open `and twice the gain will be realized.

It appears that for a broadband power amplifier, a duplex distributed amplifier will make a more eicient amplifier from the standpoint of power output and a broader space coverage for an aircraft jammer installation. It must be noted, however, that the only power gained is that originally lost in the reverse termination; the overall eiciency is thereby increased.

For purpose of exemplifcation a particular embodiment of the invention has been shown and described according to the best present understanding thereof. However, it will be apparent to those skilled in the art that various changes and modications in the construction and arrangement of the component parts thereof can be resorted to Without departing from the true spirit and scope of the invention.

I claim:

1. A broadband jammer comprising a pair of spaced apart antennas substantially shielded from each other, a

d duplex power amplifier constituted by a distributed amplifier including a plate line, the opposite ends of said plate line being connected to the respective antennas, a grid line and a voltage wave input in the center of said grid line.

2. A broadband jammer comprising a pair of antennas substantially shielded from each other, a broadband distributed amplier connected between said antennas, said amplifier including a plate line having the opposite ends connected to the respective antennas, a grid line and a voltage input connection centrally of said grid line.

3. A distributed amplifier including a plurality of pairs ot' current generator tubes, a plate delay line connected to the plates of said tubes, a load connection at each end of said line, a grid delay line, an input voltage connection centrally of said grid line for propagating a voltage simultaneously in opposite directions in said amplifier.

References Cited in the file of this patent UNITED STATES PATENTS 2,530,142 Atkins Nov. 14, 1950 2,593,948 Weigand Apr. 22, 1952 2,658,992 Byrne Nov. 10, 1953 2,863,007 Fischer Dec. 2, 1958 2,885,543 Williams May 5, 1959 2,960,664 Brodwin Nov. 15, 1960 FOREIGN PATENTS 739,954 Great Britain Nov. 2, 1955 954,073 Germany Dec. 13, 1956 

1. A BROADBAND JAMMER COMPRISING A PAIR OF SPACED APART ANTENNAS SUBSTANTIALLY SHIELDED FROM EACH OTHER, A DUPLEX POWER AMPLIFIER CONSTITUTED BY A DISTRIBUTED AMPLIFIER INCLUDING A PLATE LINE, THE OPPOSITE ENDS OF SAID PLATE LINE BEING CONNECTED TO THE RESPECTIVE ANTENNAS, A GRID LINE AND A VOLTAGE WAVE INPUT IN THE CENTER OF SAID GRID LINE. 